In recent years, the increasing trend for healthier diets has increased demand for more fruits and vegetables, which continues the need to farm in fields that are infested with soil-borne plant pathogens, insects, weeds and/or parasites, such as nematodes. Soil fumigation is often the best or only economical method of reducing those pest populations sufficiently to produce high quality and high yielding crops. In a representative soil fumigation protocol, a fumigant that includes one or more volatile substances is provided in compressed gas cylinders and shank-injected into the soil, for example, about 6 to 18 inches deep using a positive pressure closed system (for example, pressurized with nitrogen gas). In other fumigation methods, the volatile substances are applied to the soil by surface spraying or dripping. The soil is then covered, for example by a plastic sheet, to reduce the loss of fumigants into the atmosphere, which would result in loss of fumigant efficacy. For example, a polyethylene sheet can be laid down over the soil immediately behind the shanks of the injection equipment or immediately behind the sprayer or drip application equipment. The polyethylene sheet, although not impermeable to gases, can reduce the dissipation rate of gases into the air, and thus reduce the depletion of the volatile fumigants by dissipation into the atmosphere. Application of the plastic sheet is also referred to as “mulching” or “tarping” the soil. One example of plastic sheeting that is commonly used for soil mulching is high density polyethylene (HDPE). The end goal is for the volatile substances in the soil to effectively reduce or eliminate the pathogens, insects, weeds, parasites or other pests.
One problem with the soil fumigation approach, however, is that some of the volatile substances in the fumigants escape into the atmosphere. Government regulations have been implemented that require a “buffer zone” of a predetermined size around an area undergoing a fumigation treatment (i.e., application site) when certain fumigants are used, to reduce risks. A buffer zone provides distance between the application site (i.e., edge of a field being treated) allowing airborne residues to disperse with less risk. The size of a given buffer zone is based on the following factors: (1) fumigant application rate; (2) field size; (3) application equipment and methods; (4) fumigant used; and (5) emission-control measures (e.g., tarps). Buffer zone distances are scenario-based using applicable site conditions. Practices that reduce emissions (for example, use of high-barrier tarps) can result in significantly reduced buffer distances and reductions in the amount of fumigant needed to successfully control soil-borne pests.
In view of the above and other factors, there is a need for new fumigation methods that reduce the amount of fumigant necessary to achieve a desired end result, reduce the amounts of volatile substances that pass into the atmosphere following a fumigation treatment or application of other volatile substances, and reduce the size of buffer zones around application sites. The present inventions address these needs.